OXIDATION OF CARBON COMPOUNDS BY SiO2-DERIVED OXYGEN WITHIN LASER-INDUCED VAPOR CLOUDS

Introduction: Hypervelocity impacts on the surface of growing planets may generate impact-induced vapor clouds and many chemical species are produced within such vapor clouds. These species may control the surface environments of the planets, such as temperature and redox state of the atmosphere. It is, thus, important to understand the composition of gases produced within an impact-induced vapor cloud. However, chemical reactions in a vapor cloud are so complicated that the composition of produced gases is poorly known. In particular, chemical reactions between silicates and carbon compounds are not understood well. In the previous theoretical studies on gases generated within a impact-induced vapor cloud, only the volatile components are considered; effects of silicates are ignored [e.g., 1-3]. This is because silicates are assumed to condense and not to participate in the reactions among carbon compounds. However, Mukhin et al. [4] suggested that oxygen released from silicates reacts with carbon compounds within a vapor cloud. They irradiated pulsed laser on terrestrial rocks and chondrites to simulate impact vaporization and showed that the gas products within vapor clouds are composed mainly of oxidized species, such as CO and CO 2. They proposed that oxygen derived from thermal decomposition of silicates oxidizes carbon. However, the oxidation process has not been investigated in detail. No clear evidence that indicates oxidation of carbon by silicate-derived oxygen has been presented. Also, we do not know which molecular species in silicates supply oxygen to oxidize carbon. Thus, it is still uncertain whether silicate-derived oxygen really plays a key role in chemical reactions within a vapor cloud. A large amount of silicates are contained in asteroids (or even in comets) and in surfaces of terrestrial planets. Thus, if silicate-derived oxygen affects the reactions among carbon compounds in a vapor cloud, the composition and oxidation state of produced gases should be influenced very much and differ greatly from the composition predicted by the theoretical studies that neglect effects of silicates. In this study, in order to examine whether oxygen derived from thermally decomposed SiO 2 , which is a main component of silicates, reacts with carbon compounds within a vapor cloud, we conducted laser-pulse heating experiments using mixtures of SiO 2